Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 404,331	$ 385,426	$ 1,191,094	$ 1,170,512
Credit loss expense	19,386	11,185	48,823	30,190
Total non-interest income	113,707	105,998	336,274	314,791
Total non-interest expense	323,410	293,256	966,591	863,440
Income (loss) before income taxes	175,242	186,983	511,954	591,673
Income tax expense (benefit)	28,741	31,332	84,264	96,251
Net income (loss)	146,501	155,651	427,690	495,422
Preferred stock dividends	1,668	1,668	5,006	5,006
Net income (loss) available to common shareholders	144,833	153,983	422,684	490,416
Revenues from (expenses to) external customers	518,038	491,424	1,527,368	1,485,303
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	405,605	386,832	1,195,680	1,172,689
Credit loss expense	19,386	11,185	48,823	30,190
Total non-interest income	66,048	62,518	194,606	183,969
Total non-interest expense	281,631	254,747	844,657	751,539
Income (loss) before income taxes	170,636	183,418	496,806	574,929
Income tax expense (benefit)	28,363	31,021	82,817	93,775
Net income (loss)	142,273	152,397	413,989	481,154
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	142,273	152,397	413,989	481,154
Revenues from (expenses to) external customers	471,653	449,350	1,390,286	1,356,658
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	2,086	2,018	5,662	5,762
Credit loss expense	0	0	0	0
Total non-interest income	48,144	43,903	143,059	132,088
Total non-interest expense	40,584	37,304	116,432	106,811
Income (loss) before income taxes	9,646	8,617	32,289	31,039
Income tax expense (benefit)	2,026	1,809	6,781	6,518
Net income (loss)	7,620	6,808	25,508	24,521
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	7,620	6,808	25,508	24,521
Revenues from (expenses to) external customers	50,230	45,921	148,721	137,850
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(3,360)	(3,424)	(10,248)	(7,939)
Credit loss expense	0	0	0	0
Total non-interest income	(485)	(423)	(1,391)	(1,266)
Total non-interest expense	1,195	1,205	5,502	5,090
Income (loss) before income taxes	(5,040)	(5,052)	(17,141)	(14,295)
Income tax expense (benefit)	(1,648)	(1,498)	(5,334)	(4,042)
Net income (loss)	(3,392)	(3,554)	(11,807)	(10,253)
Preferred stock dividends	1,668	1,668	5,006	5,006
Net income (loss) available to common shareholders	(5,060)	(5,222)	(16,813)	(15,259)
Revenues from (expenses to) external customers	$ (3,845)	$ (3,847)	$ (11,639)	$ (9,205)